1. Field of the Invention
The present invention relates to a pod cover removing-installing apparatus for a pod which contains and transfers thin substrates such as semiconductor wafers from one space to another space while maintaining the cleanliness of both spaces.
2. Description of the Background Art
FIG. 21 shows an example of a conventional pod cover removing-installing apparatus.
This conventional pod cover removing-installing apparatus 100 is provided with a diaphragm 101 which partitions off a high clean space A and a low clean space B, an opening 102 formed in the diaphragm 101 that serves as a passage between the high clean space A and the low clean space B, a door 103 which opens and closes the opening 102 of the diaphragm 101, a latch mechanism 104 that latches the cover 203 of the pod 200 with two positioning pins 104a, 104b and two T-shaped keys 104c, 104d provided in the door 103, and a table 105 provided in the low clean space B for mounting the pod 200, which has three positioning pins 105a, 105b, 105c and one lock key 105d. 
The pod 200 is a container with an extremely clean internal space C for containing a plurality of semiconductor wafers (25 wafers, for example).
This pod 200 is provided with a main container body 201, an opening 202 provided on one side of the main container body 201, a cover 203 for opening and closing the opening 202, the cover 203 having pin holes 204a, 204b for engaging the positioning pins 104a, 104b, and key holes 204c, 204d for engaging T-shaped keys 104c, 104d, and a bottom 205 having grooves 205a, 205b, 205c possessing a V-shaped section for engaging the positioning pins 105a, 105b, 105c, and a key hole 205d for engaging the lock key 105d. 
When the pod 200 is placed on the table 105, the three positioning pins 105a, 105b, 105c engage the V-shaped section-possessing grooves 205a, 205b, 205c. In this instance, switching on a lock button, not shown in the drawing, causes the lock key 105d to move upward, become angled, and engage the key hole 205d. Then, the table 105 moves toward the diaphragm 101 for a prescribed distance (about 30 mm, for example), thereby causing the pod 200 to become attached to the diaphragm 101. A sealing material such as an O-ring, not shown in the figure, is provided along the circumference of the opening 102 of the diaphragm 101 and the opening 202 of the pod 200, to ensure close attachment of the openings and maintain cleanliness.
The movement of the table 105 causes the cover 203 of the pod 200 to become closely attached to the door 203, whereby the positioning pins 104a, 104b engage the pin holes 204a, 204b of the cover 203 and the T-shaped keys 104c, 104d engage the key holes 204c, 204d. Thereafter, the T-shaped keys 104c, 104d are rotated 90° by a rotary actuator or the like, not shown in the figure, whereby nails 204e to 204h are pulled in to release the lock between the container main body 201 and the cover 203.
Then, the door 103 is pulled into the space A (arrow D1) and caused to descend (arrow D2) by a drive mechanism, not shown in the figure, whereby the internal space C of the pod 200 and the internal space A of the partition board 101 are brought into communication while maintaining cleanliness.
In the conventional technology mentioned above, the pod 200 is made from a resin by molding. Because the formed article may be distorted depending on molding conditions or temperatures, the positioning pins 104a, 104b, the pin holes 204a, 204b of the cover 203, and the key holes 204c, 204d are tapered to ensure a smooth removing-installing operation.
However, when wafers with a large diameter (exceeding 300 mm) are placed in the pod 200, a very stringent standard is necessary to secure an allowable distortion error of ±0.5 mm. For this reason, significant difficulties may be encountered for performing the above operation in a stable manner. The following countermeasures are considered to overcome this problem.
(A) One method is to precisely fabricate and adjust each pair of the main container body 201 and cover 203, and assemble the apparatus using such a pair of the main container body 201 and cover 203. However, this method requires readjustment of the apparatus when another pod is used.
(B) Another method is to absorb a deviation between the main container body 201 and the cover 203 by designing the main container body 201 to be slightly movable. This method is effective for a small distortion, but ineffective for a large distortion. For example, even if there are no problems when the apparatus is new, distortions will be produced in two or three years after fabrication and the apparatus may not operate smoothly as time goes by.
An object of the present invention is to provide a pod cover removing-installing apparatus for a pod which can open and close any cover for a variety of pods made, according to the SEMI standard, by a variety of manufacturers. These pods can satisfy an allowable distortion error and are capable of being normally operated even if conditions such as temperature, humidity, and use for such a variety of pods change, and the covers of these pods can be removed and installed without causing it to collide with any one of the parts of the pods.